This invention relates to a method and apparatus for supplying predefined quantities of bulk material to a packaging system and, more particularly, a multi-stage process of weighing and discharging bulk materials which provides improved accuracy of final product weight.
Several methods and devices for automatically filling shipping packages with bulk materials are practiced in the industry. A significant problem with automatic filling methods, however, is obtaining accurately weighted portions of bulk material to be packaged. Various methods and devices relative to this problem have been proposed in the prior art which vary the discharge rates of loss-in-weight feeders by comparing actual discharge rates with a desired discharge rate. Another method, disclosed in U.S. Pat. No. 5,466,894 to Naef, proposes differential weighing of a quantity of material prior to discharging the material for packaging.
Although assumably effective in operation, such known devices and methods fail to account for weight variances introduced when a loss-in-weight feeder is filled with a weight of bulk material that is significantly heavier than the desired package weight. Further, loss-in-weight feeders presently do not protect sensitive weighing mechanisms from damage caused by overloading so as to ensure weighing accuracy. Thus, it is desirable to have a process for weighing and delivering an amount of bulk material to a loss-in-weight feeder which closely approaches the desired package weight prior to utilizing the feeder which then supplies an extremely accurate portion for packaging. It is also desirable to deliver a generally accurate package amount of material to the feeder so as to protect the sensitive weighing mechanisms from damage.